1. Field of the Invention
This invention generally relates to a high-frequency switch module, and more particularly, to a high-frequency switch module used for a front end module of multiple communication systems.
2. Description of the Related Art
In recent years, mobile telephones, for example, have been upgraded in functions and services. As part of the example, mobile telephones that can utilize multiple communication systems have been proposed.
Communication devices as represented by the above-mentioned mobile telephones are required to establish communication at different frequency ranges. Recently developed triple-band mobile telephones are able to communicate with three transmission and reception systems such as GSM (Global System for Mobile Communications) system, DCS (Digital Communications System) system, and PCS (Personal Communications Service) system.
However, the above-mentioned GSM, DCS, and PCS systems utilize different frequency ranges; therefore the mobile telephone is equipped with a switch for switching the frequency ranges to utilize these systems.
A high-frequency switch module having a separator and a PIN diode switch circuit for switching the frequency ranges has been proposed, as disclosed in Japanese Patent Application Publication No. 2002-101005 and Japanese Patent Application Publication No. 2002-64301. FIG. 1 shows a high-frequency switch module 900, which is an example of the above-mentioned high-frequency switch module.
Referring to FIG. 1, the high-frequency switch module 900 includes a separator/combiner 901 connected to an antenna 909, two PIN diode switch circuits 902 and 903 connected to the separator/combiner 901, a low-pass filter (hereinafter simply referred to as LPF) 904a and a band-pass filter (hereinafter simply referred to as BPF) 905a connected to the PIN diode switch circuit 902, a LPF 904b, a BPF 905b, and a BPF 905c, which filters are connected to the PIN diode switch circuit 903.
The separator/combiner 901 separates high-frequency signals inputted from the antenna 909, and then applies each of the separate signals to the PIN diode switch circuit 902 or 903. At the same time, the separator/combiner combines the high-frequency signals from the PIN diode switch circuits 902 and 903, and applies the combined signals to the antenna 909. The PIN diode switch circuit 902 selects one of the LPF 904a and the BPF 905a in order to selectively use two frequency ranges. The PIN diode switch circuit 903 selects one of the LPF 904b, the BPF 905b, and the BPF 905c in order to selectively use three frequency ranges. With the above structure, the high-frequency switch module 900 can handle the three transmission and reception systems.
However, the above-mentioned high-frequency switch module requires the separator/combiner in order to selectively use the three transmission and reception systems. Therefore, the module needs a large number of components and has a difficulty in downsizing.
Besides, generally, the high-frequency switch module equipped with the separator/combiner and the PIN diode switch circuit is required to cause a sufficient amount of current to flow in the PIN diode switch circuit in order to realize a low insertion loss. However, this circuitry consumes a large amount of power. This causes a serious problem, particularly, for battery-driven electronic devices such as mobile telephones because the battery is exhausted faster.
There is a proposal to solve the above-mentioned problem, as disclosed in Japanese Patent Application Publication No. 2003-18039. The proposal employs a gallium arsenide (GaAs) switch, which is less power consumable than the PIN diode switch circuit.
However, the GaAs switch has a small amount of stopband attenuation. The high-frequency switch module equipped with the GaAs switch has a problem in that a transmission and reception system in a selected state might be affected by another transmission or reception system.